1. Field of the Invention
This invention relates to the pressure casting of solid propellant rocket motors, and in particular, to such casting where the solids and the liquids of the propellant are mixed although uncured prior to loading in a motor.
2. Description of the Prior Art
Various forms of apparatus for use in casting uncured propellant in the motor case of a solid propellant rocket motor are known in the prior art. One such apparatus, as disclosed in U.S. Pat. No. 3,186,035 granted on June 1, 1965 to G. K. Grace and assigned to the assignee of the present invention, includes a core and surrounding barrier sleeve that are concentrically positioned within the motor case. The apparatus is intended for use in large motors such as a monolithic shuttle booster containing 100,000 pounds of propellant or more, and involves pulling of the core during loading. When the core and barrier are in position, the uncured propellant is cast into the motor case by means of a casting bayonet. The casting bayonet disclosed is of a type known in the art as a "fire hose bayonet." This bayonet allows propellant to flow around the core but does not place the propellant uniformly around the core. That is to say, the propellant must flow from where it is deposited to the other side of the core.
In my pending application Ser. No. 000288 filed jointly with C. B. Dye, on Jan. 2, 1987 and the disclosure of which by reference is incorporated herein, there is disclosed a bayonet, hereinafter termed an "annular bayonet," for casting uncured solid propellant in solid propellant rocket motors in which the exit end is modified so that exiting propellant passes through thin annular slit-like openings. The propellant, being a non-Newtonian Power Law fluid, becomes more fluid flowing through thin slits than through a circular opening. This improves the fluidity and self-leveling behavior of the fluid. Both of these effects promote the elimination or reduction of a tendency for air to be trapped in the cast propellant and enables uniform placement of the propellant around the core. The annular bayonet has particular utility for small tactical motor castings which typically hold 100 pounds or less of propellant.
There has been a problem in the prior art in the use of the annular bayonet in respect of a tendency for pockets of air to adhere to the inner cylindrical wall thereof even after pressure purging with propellant, that is, running propellant in excess amounts through the bayonet to sweep out the air. Such trapped pockets of air eventually come out, however, and form voids in the cast propellant. Another problem, in this connection, aside from the waste of propellant involved and the cost thereof, is the disposal of such waste propellant and the cost of such disposal.
Thus, there is a need and a demand for improvement in the method of and apparatus employed for purging the annular bayonet of air preparatory to the use thereof in the pressure casting of propellant in a rocket motor to the end of eliminating voids in the cast propellant and minimizing the cost of purging, which cost not only involves propellant wastage but also clean-up. The present invention was devised to fill the technological gap that has existed in the art in these respects.